Glossary & Jargon

bao1x - The Baochip-1x SoC.

baosec - Internal development name of a fully-featured hardware password manager based on the bao1x SoC.

betrusted-soc - The name of the FPGA-based SoC that powers Precursor

BDMA - BIO DMA (Direct Memory Access). DMA mediated by a BIO CPU.

BIO - Bao I/O. A quad-core Risc-V, register-mapped I/O processor with register-mapped inter-processor communication FIFOs.

blocking - A message type that stalls program execution until it returns.

boot0 - On bao1x, a small, indelible code stub that sets up initial security and checks the validity of boot1.

boot1 - On bao1x, an updateable machine-mode program that mediates firmware updates, audits and security.

CID - A connection ID. In order to keep SIDs secret, the CID is effectively a lookup table to SIDs that is maintained by the kernel.

dabao - A breakout board for the bao1x targeted at developers and system integrators.

Drop - A trait in Rust that is called when an object goes out of scope. Frequently used in Xous to automatically respond to blocking message types.

client - Any program attempting to talk to a server. Servers can be clients of other servers. Even the kernel can be a client of another server.

connection - A routable path between a client and a server. There can be up to 32 connections per PID.

HAL - Hardware abstraction layer.

hosted mode - An emulation mode for Xous where the kernel runs on your local PC

keystore - A userspace service that manages security keys for the bao1x platform. Must be at PID 3 when present. In Sv32 mode, the underlying hardware is aware of the current PID and will deny access to data slots if the wrong PID is running. Note that bootloaders have free reign of the system.

lend - In the context of memory messages, a page of memory that has been mapped into a server's address space and marked as read-only. The page is returned to the caller when the message is Dropped by the server.

loader - A program that runs in machine mode that copies the initial process set and sets up virtual memory for the kernel.

memory message - A message that uses virtual memory pages to communicate. A full page of memory is mapped into the target server's process space. The page can be send, lend, or mutable lend type.

message - An abstract type that is used to communicate between clients and servers. Messages can be scalar or memory, blocking and nonblocking.

mutable lend - In the context of memory messages, a page of memory that has been mapped into a server's address space and marked as read/write. The page (and any updated data within) is returned to the caller when the message is Dropped by the server.

nonblocking - A message type that continues execution without waiting for the receiver to acknowledge receipt. Basically, async communications. Scalar messages are assumed to be non-blocking unless specified as blocking.

page - The smallest mappable unit of memory in Sv32. In Xous, this is set to 4096 bytes.

Precursor - A fully-featured system for password management built around the betrusted-soc FPGA design. See precursor.dev.

scalar message - A message whose arguments fit entirely within the available registers of the CPU (maximum of 5, 32-bit arguments). Scalar messages are distinguished from memory messages in that they are much faster to send and return.

send - In the context of memory messages, a page of memory that has been mapped into server's address space with no expectation of return. The page now belongs to the target server forever, until it Drops the page.

thread - A scheduled unit of computation. Each PID can have up to 30 threads. Note that thread 0 is always present and it is the interrupt handler thread.

TID - The ID number of a thread. TID 0 is the interrupt handler thread.

PID - The process ID. This defines an isolated virtual memory name space. There can be up to 255 PIDs in Xous, where PID 1 is always the kernel (PID 0 is not valid). As a rule, each service is located in its own PID, but for tightly coupled services more than one can be packed into a PID.

server - A routable messaging endpoint, specified with a 128-bit server ID. The server ID may be randomly generated, in which case, it is considered secret and not directly discoverable; it has to be looked up and approved via xous-names.

service - A collection of servers that provide a service. Generally confined to a single PID. As a microkernel, many functions traditionally provided by a monolithic kernel are actually provided by userspace services. Examples: ticktimer, xous-names.

Sv32 - The RISC-V standard for virtual memory using 32-bit addresess and 2-level page tables.

target (Rust) - A compiler specification in the form of <architecture>-<vendor>-<os>-<abi>. Example: riscv32imac-unknown-xous-elf

target (Xous) - A specific combination of board & application software, yielding a binary image that can be programmed onto the board. Examples: baosec, dabao, app-image.

ticktimer - The equivalent of a scheduler in monolithic kernels. ticktimer implements sleeps, mutex's, and elapsed time sense for the overall system.

TOFU - Trust On First Use. A method for limiting access where the first contact is considered to be the only trusted contact: requires a strong assumption that the boot environment is safe.

xous-log - A service that provides console logging and interaction.

xous-names - A lookup service that can translate free-form utf-8 strings that name a service into CIDs. Internally, xous-names maintains a lookup table between the server name and its SID, along with a count of connections to the server. It can enforce a maximum connection limit, enabling a TOFU-style access control between trusted and untrusted services.

xous-swapper - A userspace service that manages swap memory on behalf of the kernel. Must always be at PID 2 when present.